1. Field of the Invention
The present invention pertains to devices for cutting elastomeric materials; and, more particularly, pertains to such devices for in situ sampling of specimens of solid propellant in a rocket motor.
2. Description of the Prior Art
Large, military, solid propellant, rocket motors must be stored for decades and yet function with full effectiveness. To ensure this effectiveness, samples of the propellant are taken regularly from substantially complete serviceable or specimen motors for testing to determine if the propellant has remained stable. The propellants of interest are elastomers which are very tough and elastic so as to retain their shape and function despite shocks in transportation and the intense vibrations and thermal stresses that occur following ignition. The propellant is, typically, a single large "grain" cast within a generally cylindrical casing.
Because of the mechanical properties of these elastomeric propellants, the large size of the motors and samples, the inaccessibility of the propellant within the casing, and the dangers of ignition or detonation involved in cutting energetic materials, the prior art has no completely satisfactory method or device for obtaining the necessary samples.
It is known to obtain a cylindrical specimen of such propellant adjacent to the casing by, initially, cutting an annular opening through the casing and into the propellant to form a plug or core of the propellant; and then detaching the specimen. One method of detaching the specimen is by successive cuts with a wire mounted on two hydraulically powered arms, a method ineffective with highly elastic propellant which deforms without being severed. A second method effective with highly elastic propellants uses a wire loop which is inserted into the opening about the plug and which is contracted to cut off the plug, the loop being connected at one point to a rod which is rotated to wind the wire onto the rod and thus contract the loop. However, this second method damages the specimen by embedding the rod therein and is dangerous due to subsequent uncontrolled release of resilient energy stored in the wire as it was wound onto the rod.